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Ruby Ruby Blocks Working With Blocks Block Method Practice: Custom Classes

Posted by Arjun Temurnikar
Arjun Temurnikar
9,695 Points

What am I doing wrong?

Challenge: Call the run method on the benchmarker object and pass it two arguments. The first argument should be a string of the description. The second argument can be a block with any code you choose.

simple_benchmarker.rb 
class SimpleBenchmarker
  def run(description, &block)
    start_time = Time.now
    block.call
    end_time = Time.now
    elapsed = end_time - start_time

    puts "\n#{description} results"
    puts "Elapsed time: #{elapsed} seconds"
  end
end

benchmarker = SimpleBenchmarker.new
benchmarker.run "Something" { puts "This is a block." }

I don't understand what I am doing wrong here.

1 Answer

Arjun Temurnikar
Arjun Temurnikar
9,695 Points

I found out why I was wrong.

When the run method has only one argument like so:

Class Benchmarker
  def run(&block)
    # do something
  end
end

then, this is valid ruby:

benchmarker.run { puts "This is block." }

But, when the method has 2 arguments like so:

Class Benchmarker
  def run(description, &block)
    # do something
  end
end

then, one has to use the do...end syntax to pass the block like so:

benchmarker.run "This is a description." do
  puts "This is block."
end

Namely, one cannot pass {} as an argument in a method ().

This:

run("fast", {puts "today"})

is invalid syntax.

That's why blocks are passed as &block

My mistake was that I assumed {} and do...end are ALWAYS interchangeable.

I guess this is an exception.

I am posting here so that it might be helpful to others.

Heather Stone
Heather Stone
5,784 Points

Thank you!

Dusty Longwell
Dusty Longwell
6,981 Points
Dusty Longwell
Dusty Longwell
6,981 Points

Very helpful!! I was confused as to why it would not work also. I don't think the use of & was described very well in the video.